WO2005095926A2

WO2005095926A2 - Luminescence optical method for authenticating products

Info

Publication number: WO2005095926A2
Application number: PCT/EP2005/003522
Authority: WO
Inventors: Otto S. Wolfbeis; Michaela Gruber; Petra Bastian
Original assignee: Chromeon Gmbh
Priority date: 2004-04-02
Filing date: 2005-04-04
Publication date: 2005-10-13
Also published as: WO2005095926A3; DE102004016249A1

Abstract

The invention relates to a method for carrying out luminescence optical authentication during which a product is provided with at least one luminescent marker, and the authentication ensues by determining the decay time of the luminescence of the marker.

Description

Luminescence optical process for the authentication of products

description

The invention relates to a method for luminescence-optical authentication, wherein a product is provided with at least one luminescent marker and the authentication takes place by determining the decay time of the luminescence of the marker.

Authentication Purpose

The authentication of products of all kinds is of considerable technical importance because products and goods can be marketed under false brand names, medical and technical devices can be operated with unauthorized products and reagents, and banknotes and credit cards can be counterfeited. Authentication also aims at clearly identifying products from a certain manufacturer, as well as ensuring that only well-defined products are used in certain processes. This is a very extensive problem. It includes the use of original medical technology devices and components as well as the use of original spare parts for repairs. In practice, a distinction is made between authentication with regard to a yes / no decision (e.g. the question of whether there is an authentic product or a counterfeit) and authentication with regard to product coding in the sense of an assignment (e.g. Quality characteristics, batch, production or expiry date, place of manufacture, material used, use in a measuring device only intended for this, the respective purpose).

The following products particularly often require clear authentication: textiles, clothing, plastic injection molded parts, medical Devices, disposable materials for medicine, medicines, spare parts of all kinds, automotive components and spare parts, microtiter plates for medical diagnostics and high-throughput screening, plastic packaging materials (also with regard to sorting for recycling), metal foils or paper, wood, Paper, packaged food of all kinds (milk and milk products, meat, fish, carbohydrates and the like), but also live animals. This list of eligible goods is by no means exhaustive.

State of the art

Authenticating products of any kind using fluorescent labels has a number of advantages over others, e.g. B. electromagnetic methods. In particular, this includes the fact that one can insert fluorescent markers that are not externally recognizable, but whose fluorescence can be detected with the aid of suitable measuring devices. In addition, these markers can be very small, in almost any shape and can also be inserted directly into the material (e.g. plastic). The information contained in the markers is therefore not externally recognizable and therefore hardly falsifiable.

Fluorescence markers have therefore found considerable interest. WO 2003/099039 describes phycobiliproteins that can be used to fluoresce-label bottled beer. In the US application 2003/194053, the X-ray fluorescence is used as a marking method, but it suffers from the disadvantage that a very complex and voluminous device has to be used for the detection. WO 2003/080759 uses photochromic dyes in order to use color changes due to light. Fluorescent watermark images are proposed in PCT WO 2002/098670. These materials can also only be used if the material to be marked has neither strong self-fluorescence nor is it colored. In WO 2001/090729, microtiter plates are marked by providing them with a light-sensitive compound. In the PCT WO 2001/037207 describes fluorescent markers which provide an object with coding materials which differ in size, shape and fluorescent color. Again, what has been said about the background fluorescence applies.

WO 2001/031341 provides as a marking measure a microplate on or in which a chemical reaction between the components of the microplate and the components of the product can occur. In this case, a chemical reaction between the sample and the microplate or its components must occur and lead to a change in the optical properties. PCT WO 2001/031590 provides the possibility of applying fluorescent images or characters to any product, which can be read out using an optical font reader (OCR). PCT WO 2000 / OS28631 provides for the use of lanthanide complexes as markers in the characterization of objects. Such markers have the advantage that they are themselves undyed and emit a fluorescence that is in the visible range when they are excited with UV light. PCT WO 2000/079347 provides that a material that is detected by means of fluorescence is added to a toner that is used to produce documents.

PCT WO 1998/28320 provides, inter alia, that programmable functionalized and self-arranging fluorescence-labeled nucleic acids are used to bring about product authentication or counterfeit protection. PCT WO 1997/42490 describes a method for detecting or indicating the relative proportions of key materials in products. The method is based on the interaction of these key components in products with an introduced material, the optical properties of which change with the concentration or quantity of these key products. US Pat. No. 5,292,855 provides an ink which is marked with a near infrared fluorescent dye. It consists of sulfonated polyesters and polyester amides and can be applied to a number of articles for identification or authentication. Methods for authentication are described in PCT WO 1987/06383, in which a genomic DNA is applied to the subject in question. The applied DNA is made visible by adding a fluorescent marker such as ethidium bromide. A security paper is described in US Pat. No. 4,552,617.

The method concerns - a new method for the optical marking of products, as well as markers, with the help of which this method can be carried out. The products to be authenticated are marked with one or more fluorescent or phosphorescent dyes, the decay time of the fluorescence or phosphorescence is measured and used as information for identification or authentication of a product. The decay times of the dyes can be modulated in two ways, namely either by varying the chemical structure or by adding a second substance which measurably and reproducibly changes the decay time of the fluorophore or phosphorus. Products that are provided with marking strips or dots that contain such dyes or dye combinations can be clearly authenticated, coded or assigned by measuring the decay time. The fluorescent dyes according to the invention have a decay time of at least 0.1 ns, the phosphorescent dyes have a decay time of more than 100 ns. The phosphorescent dyes are therefore also accessible to time-resolved measurement methods.

definitions

The term luminescence is used here in connection with all types of light emission, that is to say for fluorescence and phosphorescence. The term fluorescence refers specifically to rapidly decaying luminescence, that is typically in the range between 0.1 and 50 ns. The term phosphorescence refers to slowly decaying luminescence, typically in the range from 100 ns to 1 sec. In the context of this invention, a characteristic is understood to be, for example, the decay time. Further parameters of the luminescence are, for example, the absorption or emission maximum of the dyes used, and for example their relative luminescence intensity. Further parameters are mentioned in the following description.

Disadvantages of authenticating products by measuring the fluorescence intensity The intensity F of the fluorescence is comparatively easy to measure. It is related to the concentration c of the marker in the following relationship F = F ₀ ε c I φ _f where F _{0 stands} for the intensity of the light source, ε for the molar decadal absorption coefficient, / for the irradiated length of the fluorescent marker, φ _f for the Quantum yield, and k for a geometric constant. F also depends on the sensitivity of the photodetector.

However, the fluorescence intensity is not an ideal measurement or authentication variable, since it depends on the concentration c of the fluorophore added as well as on other variables in the above equation.

Advantages of authenticating products by measuring the decay time The luminescence of a luminophore usually decays according to the following exponential function: I = l ₀ e ^kt In this equation, l ₀ and / mean the intensity of the luminescence at the time zero or t, while k represents a substance-specific decay constant. This decay function is shown graphically in FIG. 1. The natural decay time τ ₀ is defined as the time in which the value l / e fell, i.e. to approximately 36.8% of the initial intensity l ₀ . The time τ ₀ can can be determined using various methods that operate either in the time domain or in the frequency domain.

The decay time τ _{0 of} the fluorescence and the phosphorescence is therefore a variable which, in contrast to the intensity, is independent of the concentration of the fluorophore or phosphorus. This gives you a measurement parameter that can be determined much more clearly than the luminescence intensity /, because it is independent of the marker concentration, the intensity of the light source, the sensitivity of the photodetector, but also of the fading phenomena that occur when the products are stored for a long time can. The ease of imitation is also much more difficult for markers that are coded over the decay time than the imitation of an (possibly even visually recognizable) absorption or emission color. Overall, τ _{0 represents} a far better parameter for authentication.

Improved authentication through time-resolved measurement of the cooldown

The measurement of the luminescence can, however, be influenced or disturbed by background luminescence. Many materials have background luminescence with decay times in the range of 0.5 to 5 ns. According to the invention, this problem can be remedied by using luminescent dyes with a decay time which is significantly longer than that of the background luminescence. The measurement (see Fig. 2) is done by determining the decay time only after a small delay phase (typically 5 - 100 ns) during which the background fluorescence has decayed sharply, while the phosphorescence is still emitting and therefore detectable becomes.

The measuring method can be refined by not only detecting the presence of the luminescence of the marker, but also determining its decay time precisely or meeting a specific requirement. A suitable quick procedure for this is that As also shown in Fig. 2, the intensity of two equally long measurement windows (Ai and A ₂ ) is determined, and the value of τ is determined using the equation τ = (t ₂ - t ₁ ) / ln (Aι / A ₂ ).

markers

The luminophores (markers) used should have the following properties: * a luminescence measurable at room temperature,

* at least one absorption band with a maximum in the range between 350 and 1000 nm,

* sufficient storage stability,

* sufficient photostability. * lack of toxicity

* Possibility of application to the product or incorporation into the product.

Possible fluorescent markers are coumarins and other oxygen-heterocyclic fluorophores, fluoresceins and rhodamines, polycyclic aromatics and quinones derived therefrom, fluorophores which are used as light collectors, and nitrogen and sulfur-heterocyclic compounds, pyrido- and indolo-aromatics, indigo dyes, cyanine - And merocyanine dyes, benzindoles and their homologues, as well as acridines, benzacridines and benzacridones.

As phosphorescent markers are metal salts, organic compounds, metal-ligand complexes, other organometallic compounds, but also more highly structured systems such. B. crystals or doped semiconductors in question. The group of phosphors mainly includes:

(1) Organic compounds that have room temperature phosphorescence (RTP), being used to increase the phosphorescence intensity It is favorable to distribute the dyes on a solid porous carrier (e.g. cellulose or silica gel) or to incorporate them in a matrix (e.g. in a solid melt of boric acid or phosphate; or else an organic polymer).

(2) metal salts, organometallic compounds or metal-ligand complexes which have an RTP and which in this case is often so strong that it is not necessary to embed them in a glass-like melt. These include metal salts of the type of CdS and EuP0 ₄ as well as preferably also phosphorescent derivatives of the ions of many metals, preferably of platinum, iridium, osmium, ruthenium, copper, silver or gold with different substituents or ligands, but also of semi-metals such as. B. of silicon or germanium. Examples of this are bis (thiophene) platinum (II), the numerous dipyridyl complexes of the ions mentioned, and the complexes of metals and semimetals with porphyrins and phthalocyanines or with other cyclic ligands of the crown ether or coronand and podand type. The complexes of the rare earth elements europium, terbium and dysprosium also provide phosphorescence that is clearly measurable even at room temperature. Specific examples of this are the complexes of Eu (III), Dy (III) and Tb (III) with tetracyclines, 3-carboxy-4-quinolones and other complexing agents.

(3) Non-luminescent, finely divided solids from the group of metals, semiconductors, salts, organic or inorganic polymers which are doped with one of the dyes mentioned under (1) to (3).

Possible uses of the method according to the invention

The markers can be used in various ways for coding or for producing coding materials (“tags”), which is set out below by way of example: (a) The marker is inserted directly into the product, e.g. B. by dissolving or dispersing in parts of the product, or in the entire product. The marking of plastic parts such as e.g. B. microtiter plates or products such. B. banknotes.

(b) The marker is first placed in a solid support made of a polymer, which is then used for the actual coding of the product. The carrier is usually designed as a strip or round surface and can then be attached to the (or in) the product in a form known per se. The marking of textiles, packaging or disposable items serves as an example.

(c) The marker or its solution is stamped or sprayed directly onto the product, after which any solvent which may be present is then evaporated.

All conceivable products and consumer goods can be marked in the above-mentioned ways. Examples include: Textiles, documents, banknotes, paper products, check and credit cards, identification cards, technical and medical devices, disposables, plastics, microtiter plates, packaging materials, fuels, pharmaceuticals, agrochemicals, food and beverages.

Purpose of authentication using the method according to the invention

Authentication by measuring the decay time of the luminescence preferably, but not exclusively, serves the following purposes:

* Evidence of the absence or presence of a luminophore with a certain cooldown with regard to possible product falsifications;

* Authentication of a product with regard to its suitability for a specific purpose. Extension of coding options

Given the abundance of products to be authenticated, however, it is desirable to expand the number of possible codes. Furthermore, increasing the number of codes that can be introduced through authentication also leads to an increased security level of a product. The following options exist for expanding the codes of the authentication method according to the invention:

(1) Many luminophores have environment-dependent luminescence. So if you embed a certain luminophore in different polymers, you get markers with different cooldowns and thus codes. The number of coding options is only limited by the resolution of the optical reader when determining the decay time.

(2) The decay time of a luminophore can also be changed in a targeted manner. For this purpose, for example, other dyes (so-called energy acceptors) are added to the luminophores, which change the decay time of the luminescence in a defined manner by taking over the optical energy of the marker luminophore and changing its decay time and luminescence intensity. The energy acceptor can be luminescent or non-luminescent. Typical combinations for luminophore-energy acceptor combinations are the pairs [ruthenium (tris) bipyridyl / bromothymol blue], [fluorescein / rhodamine-B]. A certain combination of luminophore and energy acceptor makes it possible to produce a whole set of luminophores from just one luminophore with its unique decay time, which increases the number of possible optical tags or codes enormously. The number of coding options is also limited here by the resolution of the optical reader when determining the decay time.

(3) The decay time of a luminophore can also be changed in a targeted manner by adding so-called quenchers, which reproducibly reduce the decay time of the luminescence of the marker by dynamic quenching Belittling way. The erasable luminophores include, above all, nitrogen-heterocyclic luminophores (such as the quinolines and acridines), the luminescence of which is quenched by chloride, bromide, iodide, but also by nitro compounds. The deletion obeys the Stern-Volmer equation: τ ₀ / τ = 1 + K _SV [L] where τ ₀ or τ for the decay time in the absence or presence of the

Löschers stand in a concentration [L], and K _sv the so-called stem

Volmer represents the quenching constant which is specific for the luminophore, the quencher and the polymer used.

(4) Another way of expanding the number of possible codes is to determine the absorption and / or emission maximum of one of the dyes used (luminophore or energy acceptor) in addition to the decay time. This gives you the option of using the wavelength of a dye as information in addition to the decay time of a luminophore. The number of coding options is limited here by the resolving power of the optical reader when determining the decay time and the wavelength of the absorption or emission maximum.

(5) Another way of expanding the number of possible codes is to use 2 luminophores in different mixing ratios. On the one hand, the decay times of one or both luminophores are determined, on the other hand, their relative luminescence intensity, and the ratio is formed from the two intensities. In experimental practice, this can vary between 1: 100 and 100: 1. This also results in a considerable variation.

(6) Even within a certain class of luminophores, you can set different cooldowns by varying the chemical structure. The following table gives some cooldowns of ruthenium Phosphors with different chemical structures (cited from the magazine Talanta, volume 41 (1994) pp. 985-991):

(7) By combining several luminophores with similar absorption and emission spectra, but different decay times, you can create a specific decay time pattern (no FRET, no deletion). Measurement method The marker is read using an optical reader. This is designed in such a way that it excites the marker with light and is able to measure its decay time. In addition, it can also enable the determination of the intensity or the spectral maximum of the luminescence of the marker. The preferred light source for stimulating the luminescence is the light-emitting diode, but also laser diodes, lasers or other light sources that can be switched quickly, such as. B. Xenon lamps are suitable. The decay time of the luminescence can be measured - in a manner known per se - using time-resolving methods (e.g. using short excitation pulses) or using frequency-resolving methods (e.g. using sinusoidally modulated light sources).

Figure 1. Temporal course of the decay time of the luminescence, and definition of the decay time τ as that time after which the initial intensity l _{0 of} the luminescence has fallen to the value l ₀ / e, that is to say approximately 36.8%.

Figure 2. Simple and fast method for determining the decay time from the intensities of the measurement windows Ai and A ₂ according to the specified Equation.

Figure 3. Absorption spectrum (left) and phosphorescence spectrum of the material according to Example 1 and differences in the intensities in air and in nitrogen.

Examples

Example 1: Production of a strip for phosphorescence-optical authentication

120 mg of polyacrylamide and 2 mg of the phosphorescent dye Ru (dpp) ₃ CI ₂ (obtained from Aldrich, Deisenhofen) are dissolved in 25 mL dimethylformamide (from Merck). The solution is stirred vigorously and 125 ml of water are then added dropwise. After adding about 20 mL water, the solution becomes opalescent. Then 1 mL of a solution of 36.g sodium chloride in 100 mL water is added to the solution in one pour. The cloudy suspension is centrifuged (3000 rpm, 15 min) and the red residue (after decanting) is washed twice with 50 mL of a 5% saline solution and then 3x with 50 mL water. The nanoparticles obtained in this way (generally approx. 50-200 nm) are suspended in water. 4 g of polyacrylamide are added to this suspension. The solution is spread out as a thin strip, freeze-dried and then cross-linked with formaldehyde. A water-insoluble orange-red strip is obtained which can be applied to a number of products.

The absorption and phosphorescence spectra of the strip are shown in Figure 3. It can be seen that the phosphorescence has a maximum at approximately 620 nm, and that the phosphorescence intensity under nitrogen and in air is practically identical, so that the quenching by the oxygen in the air is negligible. This streak has a cooldown of 3.6 μs. If the product has no phosphorescence, or if the measured decay time deviates from the specified value, the product is either a counterfeit or the product is for the intended use not provided.

Example 2. Detection of a Counterfeit A strip with a color (orange-yellow) which is practically identical to the strip given in Example 1 is obtained when a simple polyacrylamide strip is stained with the dye dichlorofluorescein. This strip can also be applied to any product. Externally, a product would be authenticated with each of the two stripes.

The difference arises only after measuring the decay time, which in this case is approximately 4.8 ns. To measure the decay time of the authentication strips, a short (<10 ns) pulse of light with a wavelength between 440 and 490 nm is directed onto the marker strip. The light pulse induces the fluorescence of both strips. The "wrong" strip (stained with fluorescein) has a very short decay time, which has disappeared after the time ti. Only the "real" streak has a measurable luminescence (phosphorescence) after the time ti, which can be recorded in the time window between and t ₂ . It can thus be determined whether the applied strip represents an original authentication or a forgery.

Example 3. Time-resolved measurement of the decay time (especially with disturbing or fake fluorescence)

The measurement process can be refined by accurately determining the decay time of the phosphorescence. To do this, one does not check whether a phosphorescence occurs at all, but whether the decay time of the phosphorescence meets a certain specification. A suitable quick method consists in determining the intensity of two equally long measurement windows A- and A ₂ ), as also shown in Fig. 2, and the value of τ using the equation τ = (t ₂ - t ₁ ) / ln (A ₁ / A ₂ ) determined Background fluorescence has subsided. A fluorescein-colored (counterfeit) strip is similar in color to an authentic strip and also fluoresces strongly, but has a very short decay time that has disappeared over time. Thus, it is recognized as a forgery by measuring the cooldown.

Claims

Expectations

1. A method for the luminescence-optical authentication of products, characterized in that the authentication takes place by determining the decay time of the luminescence of one or more luminescent markers attached to or in the product and optionally by determining a further parameter of the luminescence of the one or more luminescent markers ,

2. The method according to claim 1, comprising the following steps: * applying at least one luminescent marker on or in the product to be marked, * determining the decay time of the luminescence of at least one marker, * assigning the product using at least one measured decay time.

3. The method according to claim 1 or 2, comprising the following steps: * applying at least one luminescent marker on or in the product to be marked, * determining the decay time of the luminescence of at least one marker, * determining the absorption or emission maximum of at least one marker, * Allocation of the product on the basis of at least one decay time and on the basis of the absorption or emission maximum of at least one marker.

4. Method according to one of the preceding steps, comprising the following steps: * applying at least two luminescent markers on or in the product to be marked, * Determination of the decay time of the luminescence of at least one marker, * determination of the ratio of the intensities of the luminescence of two markers, * assignment of the product based on one or more decay times and the ratio of the intensities of the two luminescence caused by the two markers.

5. The method according to any one of the preceding claims 1 to 3, comprising the following steps: * application of a first luminescent marker on or in the product to be marked, * application of at least one luminescent or non-luminescent extinguishing substance which clearly influences the decay time of the first marker, * Determination of the decay time of the luminescence of the marker and, if applicable, of the luminescent eraser, * Allocation of the product on the basis of at least one decay time and optionally the ratio of the intensities of two luminescence.

6. The method according to any one of the preceding claims, characterized in that a marker is used, the luminescence of which has a decay time which is at least 2 times longer than that of the background luminescence.

7. The method according to any one of the preceding claims, characterized in that a time-resolving measuring method is used to determine the decay time of the luminescence, which consists in that the luminescence is excited with a short light pulse and the decay time only after a delay phase of at least 0.5 ns determined.

8. Luminescent substances which are suitable for authenticating products according to one of claims 1 to 7 and which are introduced in pure form, in a liquid or in a polymer onto or into the product to be authenticated or its packaging material and in this form for authentication of the products mentioned can be used by one of the methods according to the invention.

9. The method according to any one of claims 1 to 7, wherein the decay time of the one or more luminescent markers is specifically changed.

10. The method according to claim 9, wherein the decay time is changed by adding further dyes and / or by adding extinguishers.

11. The method according to any one of claims 1 to 7 and 9 to 10, wherein in addition to the decay time, the absorption and / or emission maximum of the luminescent marker is determined.